one of the hubs is broken and missing the o-ring. I can try locking them to make sure the 4 wheel drive works. If it does they I guess the vacuum circuit is bad. I just didn't know if it is better to change to full manual hubs.

I thought mine were broken, a quick tear down and lube proved otherwise. O-rings aren't hard to find, I'd start at NAPA.

On the 03 and up, if the air goes dashboard vent to windshield vent when 4HI is selected, then the vacuum system has a leak. However, even in this condition, selecting LOCK on the hubs should get front axle engagement.

Lock the hubs then try to twist the drive shaft while it's in park. That's how I find out if my hubs have unlocked after I have manually locked them. I don't trust the vacuum system all of the time. Sometimes I have to rock the u-joint on the passenger side when that hub hangs up.

I've turn stock hubs and warn premiums into metal shavings, I now have mile maker hubs.. Got them off xdp they have lasted two years of abuse, like mud pits, truck pulls, hooking chains on pavement ( how I killed the other hubs), and just heavy trails and powerlines!

Thanks everyone for their help. You won't believe what the problem was. I replaced one of the hubs, no problem. The 4 wheel drive still didn't work I checked all the vacuum circuits they were ok. It turns out the fittings on the knuckles were rusted shut. I replaced the 2 hoses and added brass fittings and the 4 wheel drive works great!!!!

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